Reflector with resistant surface

ABSTRACT

Reflectors, for example, for lamps used for technical lighting purposes, having a surface which is resistant to mechanical and chemical attack and has high total reflectivity. The body ( 10 ) of the reflector, which is, for example, a rolled aluminum product such as a foil, a strip of a sheet, has a surface layer in the form of a layer system containing (a) a pretreatment layer ( 11 ), onto which is deposited (b) a functional layer ( 12 ) with silanes, having organo-functional groups, of a metal compound, and onto which is deposited (c) a metal-containing reflective layer ( 13 ). Layer (a) is deposited on the reflector body and increases the strength of bonding to the above lying layers (a) and (b). Layer (b) effects a flattening and increase in the mechanical strength of the above lying layer (c). The pretreatment layer can be a layer produced by anodic oxidation. The functional layer (b) can be a sol-gel layer. The reflective layer (c) can be a metallic reflective layer, in some cases with one or more protective layers, which are deposited, e.g., by vacuum thin layer deposition process.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a reflector having, on a reflectorbody, a surface which is resistant to mechanical and chemical attack andexhibits high total reflectivity. The invention relates also to aprocess for its manufacture and the use of such reflectors with aresistant surface layer.

2. Background Art

Known is the production of bright finish strips e.g. of high purityaluminium or AlMg alloys based on aluminium having a purity of 99.8% andhigher, such as e.g. 99.9%, and roll surfaces that produce diffuse ordirectionally reflected light depending on the application. To increasethe directional reflectivity (degree of brightness) of such strips, itis also known to brighten the strips chemically or electrolytically,then to create a e.g. 1.5 μm thick protective layer by anodic oxidation.

Anodising processes are chemical treatments which suffer thedisadvantage of requiring considerable precaution in order to avoidcontamination of the environment The extent of these precautionsincreases with increasing thickness of the oxide layer.

The known processes have the further disadvantage that high purity,expensive bright-finish alloys based on aluminium of very high purityhave to be employed. As a result of the anodising process, the degree ofreflectivity of the surface, and with that both the total reflectivityand the directional reflectivity is lowered due to absorption anddiffuse scattering of light, in particular in the oxide layer. Thisrepresents a loss in energy.

Known from EP-A-0 495 755 are objects with surfaces of aluminium whichare suitable for the precipitation of layer systems from the gas phaseonto these surfaces. Anodising the surface is dispensed with and thelayer system described involves e.g. a bonding layer, such as a ceramiclayer, a light-reflecting layer, such as a metallic layer e.g. ofaluminium, and one or more transparent protective layers of metalliccompounds. Such layer systems exhibit a high degree of reflectivity andthe disadvantages of anodising are avoided. Such a layer system,however, suffers the disadvantage that the surfaces are very sensitiveto physical attack, such as mechanical or chemical attack e.g. bycorrosive media.

EP-A-0 568 943 describes the precipitation of a reflective layer on thebasis of aluminium or an aluminium alloy and a gel film which has beendeposited on the aluminium by means of a sol-gel process. This is also apossible way of arriving at reflective aluminium materials withouthaving to employ anodising; the layered structure described in EP-A-0568 943 is, however, not resistant to mechanical effects and corrosionto the extent desired.

BROAD DESCRIPTION OF THE INVENTION

The object of the present invention is to avoid the above mentioneddisadvantages and to propose reflectors which exhibit a reflectivityenhancing layer on their surface or part thereof. The aluminiumsubstrate and in particular the reflectivity enhancing layer should beextremely resistant to physical influences such as mechanical damage andchemical attack e.g. corrosion.

That objective is achieved by way of the invention in that the reflectorbody features as surface layer a layer system comprising

-   -   a) a pre-treatment layer, on which is deposited    -   b) a functional layer having organo-functional silanes of a        metal compound, on which is deposited    -   c) a metallic reflective layer,        where layer a) is deposited on the reflector body and increases        the strength of bonding to the layers lying above it, and        layer b) effects a flattening and an increase in the mechanical        strength of the above lying layer c).

DETAILED DESCRIPTION OF THE INVENTION

All three-dimensional shapes which exhibit at least one free surface ofa metal such as aluminium or an aluminium alloy may be employed as thebody of the reflector. This free surface is for example aluminium with apurity of 98.3% and higher, in some cases a purity of usefully 99.0% andhigher, preferably 99.9% and higher and in particular 99.95% and higher.Apart from aluminium of the above mentioned purities, the surface mayalso be an alloy. Preferred alloys are those of the AA 1000, AA 3000 andAA 5000 type. Further preferred alloys contain for example 0.25 to 5 wt.% magnesium, in particular 0.5 to 4 wt. % magnesium, or contain 0.2 to 2wt. % manganese or contain 0.5 to 5 wt. % magnesium and 0.2 to 2 wt. %manganese, in particular e.g. 1 wt. % magnesium and 0.5 wt. % manganese,or contain 0.1 to 12 wt. % copper, preferably 0.1 to 5 wt. % copper, orcontain 0.5 to 6 wt. % zinc and 0.5 to 5 wt. % magnesium, or contain 0.5to 6 wt. % zinc, 0.5 to 5 wt. % magnesium and 0.5 to 5 wt. % copper, orcontain 0.5 to 2 wt. % iron and 0.2 to 2 wt. % manganese, in particulare.g. 1.5 wt. % iron and 0.4 wt. % manganese or AlMgSi alloys or AlFeSialloys.

Especially preferred surfaces are for example of aluminium with a purityof 99.5% and higher, 99.8% and higher, or surfaces of an aluminium alloycontaining 0.5 wt. % magnesium, or containing 1 wt. % magnesium, orcontaining aluminium with a purity of 99% and 5 to 10 wt. % magnesium,in particular 7 wt. % magnesium and 6 to 12 wt. % copper, in particular8 wt. % copper. Especially preferred are also all aluminium alloys thatcan be rolled.

Examples of reflector bodies are cast parts and forged parts, inparticular rolled products such as foils, strips, plates, sheets, whichif desired may be shaped by bending, deep drawing, cold forming and thelike. Further, profiled sections, beams or other shapes may be employed.Depending on the application, the whole reflector may be of the abovementioned aluminium or aluminium alloy, or only parts thereof or surfaceregions may be of that material.

The above mentioned aluminium or aluminium alloy may also be part of acomposite, whereby it then constitutes at least one surface or only partof a surface e.g. of a composite foil or foil-laminate, or anothersubstrate of any material of choice such as e.g. plastic, metal such asAl-coated iron or steel sheet, or ceramic.

The aluminium surfaces may e.g. be produced by chemical and/ormechanical forming of the surface e.g. rolling, cold-forming, extrusionor casting followed by an after-treatment in the form of grinding,polishing, shot-peening with hard materials etc. The surfaces may becleaned e.g. between individual, multiple or all rolling passes, this inparticular to remove rolling fines. The cleaning of the surface may takeplace by conventional means e.g. chemically and/or electrochemically andacidic or alkaline.

Preferred reflector bodies are aluminium sheets or Al-coated iron orsteel sheet with a thickness of e.g. 0.2 to 0.8 mm, usefully 0.3 to 0.7mm, advantageously 0.5 mm. One example is an 0.5 mm thick, A4 aluminiumsheet of A1 99.5 (99.5% purity). If structured roll surfaces are to beused, then the surface of the roll may be structured e.g. by turning,grinding, engraving also by hand, by electron beam erosion, by laserbeam erosion, by electrolytic erosion or by blasting/peening with hardmedia.

The aluminium surfaces may also be subjected to a chemical orelectrochemical brightening process or to an alkaline pickling process.Such brightening or pickling processes are employed prior to anodising.

The aluminium surfaces may exhibit a surface roughness R_(a) e.g. of0.01 to 5 μm, preferably from 0.01 to 0.5 μm. Further advantageous,preferred degrees of roughness R_(a) are from 0.01 to 0.4 μm, inparticular from 0.03 to 0.06 μm, whereby 0.04 μm is highly preferred.The surface roughness R_(a) is defined in at least one of the DINstandards 4761 to 4768.

In accordance with the invention the present reflector features betweenthe reflector body and the reflective layer c) intermediate layers viz.,layer a) a pre-treatment layer e.g. in the form of a layer of anodicallyoxidised aluminium, and a layer b) in the form of a functional coatingwith organo-functional silanes of a metal compound e.g. in the form of asol-gel layer.

The pre-treatment layer a) may e.g. be a layer produced by chromatetreatment, phosphate treatment or by anodising. The pre-treatment layeris preferably of anodically oxidised aluminium and is in particularcreated directly from the aluminium on the surface of the reflectorbody. The pre-treatment layer a) may have a thickness e.g. of at least20 nm, usefully at least 50 nm, preferably at least 100 nm, inparticularly preferably at least 150 nm (nanometer). The greatestthickness of the pre-treatment layer a) may be e.g. 1500 nm, preferably200 nm (nanometer). The pre-treatment layer therefore is preferably 100to 200 nm thick.

For example, the pre-treatment layer a) may be an oxide layer producedby anodising which is formed in an a re-dissolving or anon-re-dissolving electrolyte. The pre-treatment layer a) may also be ayellow chromate layer, a green chromate layer, a phosphate layer or achrome-free pre-treatment layer which has grown in an electrolytecontaining at least one of the elements Ti, Zr, F, Mo or Mn.

The production of a preferred anodic oxide layer, such as on analuminium layer requires e.g. a clean aluminium surface, i.e. analuminium surface that is to be anodised must normally be subjected to aso-called surface pre-treatment prior to electrolytic oxidation.

Aluminium surfaces normally exhibit a natural oxide layer which, as aresult of their previous history are often contaminated by foreignparticles. Such foreign particles may be e.g. residue from rollinglubricants, protective oils for transportation, corrosion products orpressed-in foreign particles and the like. In order to remove suchforeign particles, the aluminium surfaces are normally chemicallypre-treated with cleaning agents that effect a certain degree of attack.Apart from acidic aqueous solutions, alkaline degreasing agents based onpolyphosphate and borate are particularly suitable for that purpose.Pickling or etching with a strongly alkaline or acidic solution such ase.g. caustic soda solution or a mixture of nitric acid and fluoric acideffects cleaning with moderate to pronounced removal of material. Inthat process the natural oxide layer and all the contaminants embeddedin it are removed. When using aggresive alkaline pickling solutions, adeposit of smut is often produced and has to be removed by subsequenttreatment with acid. Organic solvents or aqueous or alkaline cleanersdegrease the surface without removing any of the surface layer.

Further cleaning methods are degreasing the aluminium surface byplasma-oxidation, corona discharge or cleaning in an inert gas plasmasuch as Ar, He, Ne, N₂ etc.

Depending on the condition of the surface it may also be necessary toremove some of the surface by mechanical means using abrasive materials.Such a surface pre-treatment may be performed e.g. by grinding,blasting/peening, brushing or polishing, if necessary followed by achemical pre-treatment.

The further treatment for anodic oxidation is such that the reflectorbody—at least the part of the aluminium layer to be anodise—issubsequently placed in an electrically conductive fluid, theelectrolyte, and connected up to a direct current source as the anode,the negative electrode normally being stainless steel, graphite, lead oraluminium.

In the case of a non-re-dissolving electrolyte, the electrolyte may bemade such that it does not chemically dissolve the aluminium oxideformed during the anodising process i.e. there is no re-solution of thealuminium oxide. In the direct current field gaseous hydrogen is formedat the cathode and gaseous oxygen at the anode. The oxygen formed at thealuminium surface reacts with the aluminium and forms an oxide layerwhich grows in thickness during the process. As the resistance of thelayer increases rapidly with increasing thickness of the barrier layer,the flow of current falls accordingly and the layer ceases to growfurther.

The electrolytic production of such layers a) allows the thickness ofthe layer to be regulated very precisely. The maximum thickness ofaluminium oxide barrier layer achieved is in nanometers (nm)approximately the value of the applied voltage (V), i.e. the maximumthickness of layer is linearly dependent on the anodisingvoltage—whereby the voltage drop at the outer layer has to be taken intoconsideration. The exact value of the maximum layer thickness achievedas a function of the applied direct voltage U and—taking into accountthe voltage drop at the outer layer—can be determined by a simple trialand lies in the region of 1.2 to 1.6 nm/V. The exact value of layerthickness is a function of the applied voltage, the electrolyte usedi.e. its composition and its temperature.

In order to take into account the changing drop in voltage at the outerlayer during the process, the anodising voltage may be increasedcontinuously or stepwise during the process. The optimum anodisingvoltage, or the optimum series of voltages throughout the process andthe duration of anodising, may be determined by means of simple trialsor by measuring the reflectivity during the anodising process.

The electrolytic oxidation may be carried out in one single step byapplying a pre-defined anodising voltage or by continuously or stepwiseincreasing the anodising voltage to a predetermined value or to a valuewhich is determined by measuring the optimum reflectivity properties.The electrolytic oxidation may, however, be performed in a plurality ofsteps, i.e. in several process steps e.g. applying different anodisingvoltages.

For example on employing a non-re-dissolving electrolyte the aluminiumoxide barrier layers are almost pore-free i.e. any pores formed are aresult e.g. of contaminants in the electrolyte or structural faults inthe aluminium surface layer. This is only insignificant, however, as aresult of re-solution of the aluminium oxide by the electrolyte.

Layers a) produced this way can be produced with a precisely prescribedlayer thickness, pore-free, homogenous, and with regard to theelectromagnetic radiation, transparent, in particular in the visibleand/or infra-red range.

Organic or inorganic acids, as a rule diluted with water may be used asnon-re-dissolving electrolytes for this process; these have a pH valueof 2 and more, preferably 3 and more, in particular 4 and more and 7 andless, preferably 6 and less, especially 5.5 and less. Preferred are coldelectrolytes i.e. electrolytes functioning at room temperature.Especially preferred are inorganic or organic acids such as sulphuricacid or phosphoric acid at low concentrations, boric acid adipinic acidcitric acid or tartaric acid, or mixtures thereof, or solutions ofammonium salts or sodium salts and their mixtures. Of particular valuehere are the solutions preferably with a total concentration of 20 g/lor less ammonium salt or sodium salt, usefully 2 to 15 g/l thereofdissolved in the electrolyte. Very highly preferred thereby aresolutions of ammonium salts of citric acid or tartaric acid or sodiumsalts of phosphoric acid.

A very highly preferred electrolyte contains 1 to 5 wt. % tartaric acid,to which may be added a corresponding amount of ammonium hydroxide(NH₄OH) to adjust the pH value to the desired level.

The electrolytes are as a rule aqueous solutions.

The maximum anodising voltage that may be applied is determined by thedielectric constant of the electrolyte. This is e.g. dependent on thecomposition and temperature of the electrolyte and normally lies in therange of 300 to 600 V.

The optimum temperature for the electrolyte depends on the electrolytebeing used; it is, however, in general of secondary importance withrespect to the quality of the layer c). Electrolyte temperatures of 15to 40° C., in particular 18 to 30° C., are preferred for anodising.

Preferred is an anodic oxide layer produced by anodising in anon-re-dissolving electrolyte and not sealed.

Re-dissolving electrolytes that may be employed are e.g. inorganic ororganic acids—as a rule diluted with water—such as sulphuric acid,phosphoric acid, oxalic acid, chromic acid etc. and combinationsthereof. The anodising voltage which is applied to the surface to beanodised as direct current or alternating current is normally selectedsuch that current densities of approx. 0.1 to 10 A/dm² are obtained onthe surface. The porous structures that are obtained with re-dissolvingelectrolytes may subsequently be sealed in hot water or steam, with orwithout chemical additions. Particularly tight-bonding surfaces areobtained, however, with anodic oxide layers that have not been sealed,but have instead only been rinsed with water and dried.

A particularly suitable anodisation process for use with a re-dissolvingelectrolyte is the so-called dc-H₂SO₄ process without sealing.

Layer a), the aluminium oxide layer produced by anodic oxidation, may beat least 20 nm (nanometer) thick, usefully 50 nm and more, preferably100 nm and more and advantageously 150 nm and more. The thickness of thealuminium oxide layer a) produced by anodising is, for reasons of costsand the amount of electrolyte waste produced, for example at most 1500nm, preferably at most 200 nm. The preferred thickness of the aluminiumoxide layer produced by anodising is therefore 100 to 200 nm.

The oxidation of the aluminium surface may also be achieved by coronapre-treatment and dry oxidation.

Layer b), a functional coating with organo-functional silanes of a metalcompound e.g. in the form of a sol-gel layer is deposited on layer a).

For example layer b) is 0.5 to 20 μm thick, usefully 1 to 20 μm,preferably 2 to 10 μm thick; highly preferred is a thickness of 2 to 5μm.

The functional coating b) with organo-functional silanes of a metalcompound may have been obtained e.g. by hydrolitic condensation of thefollowing components, if desired in the presence of a condensationcatalyst and/or normal additives:

-   1. at least one cross-linkable organo-functional silane of formula    (II):    R′″_(m)SiX_((4−m))   (II)    in which groups X, which may be the same or different, stand for    hydrogen, halogen, alkoxy, acyloxy, alkylcarbonyl, alkoxycarbonyl or    —NR″2 (R″=H and/or Alkyl) and the radicals R′″, which may be the    same or different represent alkyl, alkenyl, alkinyl, aryl,    arylalkyl, alkylaryl, arylalkenyl, alkenylaryl, arylalkinyl or    alkinylaryl, whereby these radicals may be interrupted by O- or    S-atoms or the group —NR″ and may bear one or more substituents from    the group of halogens and the possibly substituted amino, amide,    aldehyd, keto, alkylcarbonyl, carboxy, mercapto, cyano, hydroxy,    alkoxy, alkoxycarbonyl, sulphonic acid, phosphoric acid, acryloxy,    methacryloxy, epoxy or vinyl groups and m has the value 1, 2 or 3,    and /or one oligomer derived therefrom, where the radical R′″ and/or    the substitute must be a cross-linkable radical or substituent, in    an amount of 10 to 95 mol %, referred to the total mol number of the    (monomer) starting components;-   2. at least one metal compound having the general formula III:    MeRy   (III)    in which Me stands for a metal from the following group Al, Zr, Ti,    where y in the case of aluminium is 3 and in the case of Ti and Zr    is 4 and the radicals R, which may be the same or different, stand    for halogen, alkyl, alkoxy, acyloxy or hydroxy, where the last    mentioned groups may be replaced wholly or partially by chelate    ligands and/or one oligomer derived therefrom and/or if desired a    complexed aluminium salt of an inorganic or organic acid in an    amount of 5 to 75 mol % referred to the total mol number of the    (monomer) starting components,-   3. if desired at least one non cross-linkable organo-functional    silane of formula I:    R′_(m)SiX_((4−m))   (I)    in which groups X, which may be the same or different, stand for    hydrogen, halogen, hydroxy, alkoxy, acyloxy, alkylcarbonyl,    alkoxycarbonyl or —NR″2 (R″=H and/or Alkyl) and the radicals R′,    which may be the same or different, represent alkyl, aryl, arylalky    or alkylaryl, whereby these radicals may be interrupted by O- or    S-atoms or the group —NR″ and may bear one or more substituents from    the group of halogens and the possibly substituted amide, aldehyd,    keto, alkylcarbonyl, carboxy, cyano, alkoxy, alkoxycarbonyl, groups    and m has the value 1, 2 or 3, and/or one oligomer derived    therefrom, in an amount of 0 to 60 mol %, referred to the total mol    number of the (monomer) starting components and-   4. if desired with one or more non-volatile oxide of an element of    the main groups 1a to Va or a sub-group IIb, IIIb, Vb to VIIIb of    the periodic system which is soluble in the reaction medium, with    the exception of Al, and/or one or more compound of one of these    elements forming a non-volatile oxide under the reaction conditions,    which is soluble in the reaction medium, in an amount of 0 to 70 mol    %, referred to the total mol number of the (monomer) starting    components;    carried out such;    -   b) that an organic pre-polymer is added to this hydrolitic        condensate, whereby the reacting cross-linkable groups of the        radical R′″ and/or the cross-linkable substitutes on the radical        R′″ have the same name as the pre-polymer, and the pre-polymer        is added in an amount of 2 to 70 mol % referred to the total mol        number of (monomer) starting components;    -   c) the coating solution thus obtained is deposited on a        substrate and subsequently cured. Further details and modes of        preparation of the functional layers b) may be obtained from        EP-A 0610831 and EP-A 0358011.

The functional layer is to advantage deposited onto the pre-treatmentlayer on the reflector body by means of a sol-gel process. Thefunctional layer can be applied to the substrate by immersion, brushing,rolling, centrifugal means, spraying, so called coil coating etc. As arule silanes are employed in the functional coating. If the silanes arepartially replaced by compounds which, instead of silicon, containtitanium. zirconium or aluminium, then the hardness, density andrefractive index of the functional coating can be varied. The hardnessof the functional layer may likewise be regulated by employing varioussilanes, for example by forming an inorganic network for controlling thehardness and thermal stability, or by using an organic network toregulate the elasticity. A functional coating, that may be considered asbetween the inorganic and organic polymers, is deposited onto thealuminium substrates e.g. via the sol-gel process by hydrolysis andcondensation of alkoxides, mainly those of silicon, aluminium, titaniumand zirconium. As a result of that process an inorganic network isformed and, via corresponding derivatised siliceous esters, additionalorganic groups can be integrated in it and can be employed forfunctionalising and for creating defined organic polymer systems.Further, the sol-gel layer may be deposited also by electro-immersioncoating on the principle of cataphoretic precipitation of anamine/organically modified ceramic.

After the anodised surface of the reflector body has been coated with afunctional layer, the coating can be cured. The curing may be performedby radiation e.g. UV radiation, electron beam or laser beam radiationand/or at elevated temperature. The temperature may be increased byconvection or thermal radiation such as infra-red radiation and/or UVradiation, or by a combination of convection and radiation such as UVand/or infra-red radiation or by means of hot gas such as hot air. Thetemperature, measured at the layer lying below the functional coatinge.g. the metal layer, e.g. aluminium layer, is e.g. higher than 110° C.,usefully higher than 150° C. and preferably between 150 and 220° C. Theelevated temperature may act on the body e.g. for 10 sec. to 120 min.The convection heating may be usefully effected by striking the bodywith heated gases such as air, nitrogen, noble gases or mixturesthereof.

The layer b) i.e. the functional layer effects a flattening or smoothingof the surface. R_(a) roughness values e.g. smaller than 0.01 μm,preferably smaller than 0.02 μm, are achieved. The surface roughnessR_(a) is defined in at least one of the DIN standards 4761 to 4768. Thefunctional layer b) may be a monolayer or a multiple layer comprisinge.g. two, three or more layers. These layers may all be of the samematerial or be of different materials, in each case selected from thematerials mentioned above for the functional layer b). The multiplelayer coatings i.e. two, three or more layer coatings may be depositede.g. by depositing a first layer, pre-curing or curing this first layer,depositing the second layer and curing the second layer. A first layerthat has only been pre-cured may be cured completely along with thecuring of the second layer. If a third layer is to be deposited, thefirst and the second layer may be cured or pre-cured and the curing maybe only for the third layer, or—as required—the these underlying layersmay be cured along with the third layer. The same applies for furtherfourth or more layers. Pre-curing includes methods such as allowing thelayer(s) to dry, pre-drying under the influence of heat or radiation orby radiation or thermal treatments. The useful thickness of a two orthree layer coating is in the above mentioned range of 1 to 20 μm,whereby each individually deposited layer may have a thickness of 2 to 5μm.

The reflective layer c) is a single reflecting layer and in particular amulti-layer system, whereby the multi-layer system features a reflectinglayer such as e.g. of aluminium, silver, copper, gold, chromium, nickelor alloys containing e.g. mainly at least one of the above metals. Thethickness of the reflective layer may e.g. be 10 to 200 nm (nanometer).one or more transparent protective layers may be deposited on thismetallic layer and may be e.g. of or contain oxides, nitrides, fluoridesetc. of alkali metals, alkali earth metals, semiconductors and/ortransition metals and/or lanthanides. Also, two or more transparentprotective layers may be provided using the above mentioned metals withdifferent indices of refraction in order to reinforce the degree ofreflection as a consequence of partial light reflection at the phaseboundary of the transparent protective layers. The individual protectivelayers are typically from 1 nm thick, preferably from 40 to 200 nm thickand exhibit in particular a thickness which is a fraction e.g. λ/2 orλ/4 of the wavelength of the radiation to be reflected. Preferred is amultilayer system containing a reflective layer and at least onetransparent protective layer. Preferred are multilayer systemscomprising a metal reflective layer on top of which is a transparent λ/4protective layer of low refractive index and on top of that layer atransparent λ/4 protective layer of high refractive index. Examplesthereof are aluminium as reflective metal layer, SiO₂ or MgF₂ as lowrefractive index λ/4 layer and Ti-oxide or Ti, Pro-xide as highrefractive index λ/4 layer. An even higher degree of refraction may beobtained using a plurality of λ/4 double layers alternating with low andhigh refractive index.

The thickness of individual protective layers can be, for example, from1 nm to 150,000 nm. Examples of the thickness of the individualprotective layers are 1 nm, 2.5 nm, 5 nm, 40 nm, 50 nm, 100 nm, 187.5nm, 200 nm, 375 nm, 750 nm, 1,500 nm, 7,500 nm, 15,000 nm, 75,000 nm and150,000 nm.

The reflective layer c) and therefore the reflecting layer or thereflecting layer and further layers of the multilayer system may bedeposited on the reflector body e.g. by gas or vapour deposition invacuum, (physical vapour deposition PVD), by thermal vaporisation, bymeans of electron beam vaporisation, with and without ion support, bysputtering, in particular by magnetron sputtering or by chemical gasphase deposition (chemical vapour deposition CVP) with and withoutplasma support.

The reflective layer c) on the reflector body via layer b) serves inparticular to reflect energy in the form of waves and/or particles,usefully for reflecting radiation having wave lengths in the opticalrange, preferably visible light, in particular that having wave lengthsof 400 to 750 nm.

The reflective layer c) on the reflector body results in particular inreflectors with coated surfaces that achieve a totalreflectivity—measured according to DIN 5036—of usefully 90% and higher,in particular 94 to 96%. The reflective layer or multilayer system maye.g. be deposited on the surface in a series of process steps whichincludes: as required, degreasing the surface to be coated, enclosingthe item bearing the surface to be coated in a vacuum unit, cleaninge.g. by sputtering, glow discharge etc., if desired depositing a bondinglayer in a preliminary stage, in a first stage depositing at least atleast one light-reflecting, in particular metal layer, and in a secondand if desired a third, fourth etc. stage precipitation of a transparentlayer or if desired two, three etc. transparent layers, then removingthe coated item from the vacuum chamber.

On the reflector according to the invention there may be providedbetween the functional layer b) and the reflective layer c) anadditional—e.g. oxide or nitride containing—bonding layer. The bondinglayer may e.g. be a ceramic layer. Such layers may be of or contain e.g.compounds having the formula SiO_(x) where x represents a number from 1to 2, or AlyOz, where y/z is a number from 0.2 to 1.5. Preferred is abonding layer comprising or containing SiO_(x) where x has the abovemeaning. The oxide-containing bonding layer is typically 1 to 200 nmthick, preferably 1 to 100 nm thick. The oxide-containing bonding layermay be deposited on the surface according to the invention or on thepreviously deposited layer e.g. by gas or vapour deposition in vacuum,(physical vapour deposition), by thermal vaporisation, by means ofelectron beam vaporisation, with and without ion support, by sputtering,in particular by magnetron sputtering or by chemical gas phasedeposition (chemical vapour deposition) with and without plasma support.

The reflectors according to the invention having surfaces that bear sucha reflective layer or multilayer system exhibit excellent reflectivityfor example of electromagnetic radiation, especially electromagneticradiation in the visible light range. The optical range includes e.g.infra-red range, the visible light range, ultra violet etc. Thepreferred range for application is that of electromagnetic radiation andthereby the visible light range.

The reflection of the radiation may, depending on the application, bedirectional, scattered or a combination thereof. For that reason thereflectors according to the invention are suitable e.g. as reflectorssuch as those for radiation sources or optical equipment. Such radiationsources are e.g. lights such as work-place lights, primary lights,secondary lights, strip lights with transvers reflectors, lightelements, lighting covers, light deflecting fins or thermal radiators.The reflectors may also e.g. be mirrors or internal mirrors in opticalequipment, lighting components or thermal radiators.

In the case e.g. of rolled products such as foils, strips or sheets orin the case of fins with an aluminium layer the individual coatings—oradvantageously all of the coatings—are deposited or precipitated incontinuous processes, as a rule in so called strip-coating or coilcoating processes. The processes used for the anodic oxidation ofaluminium may e.g. be employed to create layer a). also layer b) thefunctional layer such as a sol-gel layer, may be deposited in acontinuous process, whereby the sol is deposited on the surface to betreated by immersion, spraying or by coil coating and subsequently driedor cured in a continuous oven by radiation and/or thermal treatment.Finally layer c) or the multilayer system may be deposited byevaporisation, sputtering—in each case in particular in vacuum—etc.

The reflectors according to the present invention exhibit e.g. a 5 to50% better reflectivity. The reflectors, e.g. in the form of foils,strips or sheets can also be shaped without showing hardly any cracks.The reflectors according to the invention exhibit good resistancetowards chemical, physical and in particular mechanical deteriorationsuch as mechanical damage, wear, corrosion etc. Sources of mechanicaldamage could be e.g. on cleaning the surfaces i.e. the reflectivelayers, dust, sand and the like which become trapped between thecleaning equipment and the surface or by the cleaning equipment itselfi.e. cloth, wiper, brush etc. Corrosion could originate from moisture,gases or vapours which attack the surface or penetrate below the layersand delaminate them or alter them chemically.

The present invention includes also the use of reflectors having asurface resistant to mechanical and chemical attack and high totalreflectivity for the reflection of radiation in the optical range i.e.daylight and artificial light, thermal radiation, visible light,ultraviolet light etc. Of particular importance is the use of thereflectors for reflecting visible light in particular daylight orartificial light, including UV light. The reflectors according to theinvention are e.g. suitable as reflectors or lighting elements forlighting and technical lighting purposes such as e.g. reflectors inwork-place lighting, primary lighting, secondary lighting, striplighting with transvers reflectors, lighting elements or as lightdeflecting elements etc.

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 shows schematically a section through a reflector according tothe invention.

DETAILED DESCRIPTION OF THE DRAWING

In FIG. 1, situated on a reflector body (10)—for example strip materialof metal such as aluminium—is a surface layer in the form of a layersystem comprising a pretreatment layer (11), a functional layer (12) anda metallic reflective layer (13). The pre-treatment layer (11) may beformed directly from the material of the reflector body (10) by anodicoxidation. The surface of the pre-treatment layer (11) facing thefunctional layer (12) may exhibit some roughness. The functional layer(12) is able to even out this roughness and form a smooth surface fordeposition of the metallic reflective layer (13). The metallicreflective layer (13), or layer system comprising metal reflecting layer(17) and protective layers (16), is deposited on the functional layer(12). A ray of light (15) penetrates the transparent protective layers(16), which are sketched in here and are in particular transparent, andis reflected by the metal reflecting layer (17). In some cases a bondinglayer (14) may be provided between the functional coating (12) and themetal reflective layer (13).

Example

1. A pre-treatment layer is deposited on an aluminium strip in acontinuous process. For that purpose an aluminium strip (Al 99.8, Ra0.08 μm), 500 mm wide and 0.3 mm thick is continuously anodised at 40m/min. In that process the strip is exposed to the following treatments:

-   -   a) Degreasing at pH 9-9.5, at approx. 50° C. and bonder        V6150/01,    -   b) rinsing with tap water (room temperature),    -   c) anodising in 20% H₂SO₄ at 85° C. and 20V,    -   d) rinsing in tap water at 50° C. and    -   e) rinsing in deionised water at approx. 85° C.

The strip bearing the pre-treatment layer, in the present example thepre-anodised strip, is coated with the functional layer at 40 m/min in acoil coating process and counter-flowing immersion and deposition rollsand dried in a continuous oven at an oven temperature of 200 to 250° C.for approx. 10 to 15 sec. The temperature of the metal (measured usingthermoelements on the non-coated substrate) was between 195 and 216° C.

The rinsed strip showed no signs of interlocking and exhibited ahardness of 2H-3H measured according to the method “Pencil test afterWolf Wilburn” SNV 37113, SIS 18 41 87, NEN 5350, MIL C 27 227, ECCA testmethods, at a layer thickness of 5 μm.

The bond strength was measured according to the cross-hatch test (ISO2409). After folding, the layer exhibited regular cracks parallel to theknee of folding, but no signs of delamination.

The strip, after coating with the functional coating using the soil-gelprocess is provided with a PVD reflectivity enhancing coating (AntiflexB® of Balzers) and exhibits the following reflectivity values acc. toDIN 5036 Part 3:

Total reflectivity>95% and scattered reflectivity<1%.

The PVD layer is securely attached to the substrate and does not freeitself from the functional coating even after pronounced deformation bye.g. folding.

1. A reflector, having a surface which is resistant to mechanical andchemical attack and has high total reflectivity, wherein the metal body(10) of the reflector has a surface layer in the form of a layer systemcomprising: (A) a pretreatment layer (11), which is (i) an oxide layerproduced by anodizing with forming in a redissolving or non-redissolvingelectrolyte, or (ii) a yellow chromate layer, a green chromate layer, aphosphate layer or a chrome-free layer formed in an electrolytecontaining at least one of the elements Ti, Zr, F, Mo and Mn, onto whichis deposited: (B) a functional layer (12) of a silane, having at leastone organo-functional group of a metal compound, and said functionallayer comprising one or more layers of materials which have beenobtained by hydrolytic condensation, optionally in the presence of acondensation catalyst and/or normal additives, of the following startingcomponents: (a) at least one cross-linkable silane, having at least oneorgano-functional group, of formula (II):R′″_(m)SiX_((4−m))   (II) in which groups X, which are the same ordifferent, stand for hydrogen, halogen, alkoxy, acyloxy, alkylcarbonylor —NR″₂, wherein each R″ is hydrogen or alkyl, and the radicals R′″,which are the same or different, represent alkyl, alkenyl, alkinyl,aryl, arylalkyl, alkylaryl, arylalkenyl, alkenylaryl, arylalkinyl oralkinylaryl, whereby these radicals can be interrupted by O- or —S atomsor the group —NR″ and optionally bear one or more substituents from thegroup consisting of halogens and optionally substituted amino, amide,aldehyde, keto, alkylcarbonyl, carboxy, mercapto, cyano, hydroxy,alkoxy, alkoxycarbonyl, sulfonic acid, phosphoric acid, acryloxy,methacryloxy, epoxy and vinyl groups, and m has the value 1, 2 or 3,and/or one oligomer derived therefrom, where the radical R′″ and/or thesubstituted must be a cross-linkable radical or substituent, in anamount of 10 to 95 mol percent, referred to the total mol number ofmonomers of said starting components; (b) at least one metal compoundhaving the general formula III:MeR_(y)   (III) in which Me is Al, Zr or Ti metal, where y in the caseof aluminum is 3 and in the case of Ti and Zr is 4, and the radicals R,which are the same or different, stand for halogen, alkyl, alkoxy,acyloxy or hydroxy, where the last mentioned groups are replaced whollyor partially by chelate ligands and/or one oligomer derived therefromand/or optionally a complexed aluminum salt of an inorganic or organicacid in an amount of 5 to 75 mol percent, referred to the total molnumber of monomers of said starting components, (c) optionally at leastone non cross-linkable silane, having at least one organo-functionalgroup, of formula I:R′_(m)SiX_((4−m))   (I) in which groups X, which are the same ordifferent, stand for hydrogen, halogen, hydroxy, alkoxy, acyloxy,alkylcarbonyl, alkoxycarbonyl or —NR″₂, wherein each R″ is hydrogen oralkyl, and the radicals R′, which are the same or different, representalkyl, aryl, arylalkyl or alkylaryl, whereby these radicals can beinterrupted by O- or S-atoms or the group —NR″ and can bear one or moresubstituents from the group consisting of halogens and optionallysubstituted amide, aldehyde, keto, alkylcarbonyl, carboxy, cyano, alkoxyand alkoxycarbonyl groups, and m has the value 1, 2 or 3, and/or oneoligomer derived therefrom, in an amount of 0 to 60 mol percent,referred to the total mol number of the monomers of said startingcomponents, and (d) optionally one or more non-volatile oxides of anelement of the main groups Ia to Va or sub-groups IIb, IIIb and Vb toVIIb of the periodic system which is soluble in the reaction medium,with the exception of Al, and/or one or more compounds of one of theseelements forming a non-volatile oxide under the reaction conditions,which is soluble in the reaction medium, in an amount of 0 to 70 molpercent, referred to the total mol number of monomers of said startingcomponents, carried out such that: (1) an organic prepolymer is added tothis hydrolytic condensate, whereby reacting cross-linkable groups ofthe radical R′″ and/or the cross-linkable substitutes on the radical R′″are linkable to those of the prepolymer or are identical to those of theprepolymer, and the prepolymer is added in an amount of 2 to 70 molpercent, referred to the total mol number of monomers of said startingcomponents, and (2) the coating solution thus obtained is deposited on asubstrate and subsequently cured, onto which is deposited: (C) a metalcontaining reflective layer (13), where layer (A) is deposited on thereflector body and increases the strength of bonding to the above lyinglayers (B) and (C), and layer (B) effects a flattening and increase inthe mechanical strength of the above lying layer (C).
 2. The reflectoraccording to claim 1, wherein the pretreatment layer (A) has a thicknessin the range of 20 to 1500 nanometers.
 3. The reflector according toclaim 1, wherein the pretreatment layer (A) has a thickness in the rangeof 50 to 1500 nanometers.
 4. The reflector according to claim 1, whereinthe pretreatment layer (A) has a thickness in the range of 100 to 1500nanometers.
 5. The reflector according to claim 1, wherein thepretreatment layer (A) has a thickness in the range of 150 to 1500nanometers.
 6. The reflector according to claim 1, wherein thepretreatment layer (A) has a thickness in the range of 20 to 200nanometers.
 7. The reflector according to claim 1, wherein thefunctional layer (B) is 0.5 to 20 μm thick.
 8. The reflector accordingto claim 1, wherein the functional layer (B) is 1 to 20 μm thick.
 9. Thereflector according to claim 1, wherein the functional layer (B) is 2 to10 μm thick.
 10. The reflector according to claim 1, wherein thefunctional layer (B) is 2 to 5 μm thick.
 11. The reflector according toclaim 1, wherein the functional layer (B) is composed of a single layeror a multiple layer and the multiple layers are all of the same materialor of different materials, in each case being selected from thematerials in the functional layer (B).
 12. The reflector according toclaim 1, wherein the reflective layer (C) is a multilayer systemcomprising a reflecting layer and deposited on that transparentprotective layers with different refractive indices.
 13. The reflectoraccording to claim 1, wherein the reflective layer (C) is a multilayersystem comprising a reflecting layer and deposited thereon transparentprotective layers with different refractive indices, the reflectivelayer being 10 to 200 nm thick and each of the transparent protectivelayers being 40 to 200 nm thick.
 14. The reflector according to claim 1,wherein the reflective layer (C) is or contains a metal from the seriesAl, Ag, Cu, Au, Cr, Ni or an alloy containing mainly at least one ofthese metals.
 15. The reflector according to claim 1, wherein a bondinglayer is provided between the functional layer (B) and the reflectivelayer (C).